What is the variability of serum Insulin-like Growth Factor-1 (IGF-1) levels?

From the Guidelines

Serum Insulin-like Growth Factor-1 (IGF-1) levels can vary significantly due to various factors, including age, sex, Tanner stage, and underlying medical conditions.

Factors Affecting IGF-1 Levels

• Age and sex: IGF-1 levels are age-adjusted and sex-adjusted, and normal ranges vary accordingly 1
• Tanner stage: IGF-1 levels are also Tanner stage-matched, as levels can fluctuate during puberty 1
• Medical conditions: Certain conditions, such as hypothyroidism, malnutrition, severe infection, poorly controlled diabetes mellitus, hepatic and/or renal failure, and oral oestrogen use, can affect IGF-1 levels 1

Inter-Assay Variability

• Local Tanner stage-matched, sex-matched, and age-matched normal ranges for the IGF-1 assay must be established to avoid notable inter-assay variability 1

Clinical Interpretation

• Elevated IGF-1 levels can indicate GH excess, but marginal or mild elevation in adolescence requires cautious interpretation 1
• IGF-1 levels should be interpreted within a clinical assessment of phenotype, including height velocity, pubertal stage, and bone age 1

Biochemical Outcomes

• Elevated GH and IGF-I levels are predictors of mortality in patients with acromegaly, and normalizing IGF-I levels can result in mortality rates similar to those expected in the general population 1

From the Research

Variability of Serum Insulin-like Growth Factor-1 (IGF-1) Levels

• The variability of serum IGF-1 levels can be influenced by several factors, including age, sex, and body mass index (BMI) 2, 3.
• Studies have shown that IGF-1 levels decline with aging in adults, and there are statistically significant differences in IGF-1 levels between men and women in some subgroups of age 2.
• The reference ranges for IGF-1 levels can vary depending on the population being studied, and it is essential to establish age- and gender-specific normal ranges for different populations 2, 4.
• Biological variability and method-specific assay performance issues can also contribute to the variability of serum IGF-1 levels 5.
• Additionally, the use of different platforms for measuring IGF-1 levels can result in significant variations, highlighting the need for standardization in IGF-1 measurement 6.

Factors Influencing IGF-1 Variability

• Age: IGF-1 levels decline with aging in adults 2, 4.
• Sex: There are statistically significant differences in IGF-1 levels between men and women in some subgroups of age 2.
• Body Mass Index (BMI): Age and BMI are independent predictors of serum IGF-1 values, accounting for 39% of IGF-1 variability 3.
• Assay performance: Method-specific assay performance issues can contribute to the variability of serum IGF-1 levels 5, 6.

Clinical Implications

• The variability of serum IGF-1 levels can have significant implications for the diagnosis and management of patients with growth hormone-related disorders 4, 6.
• Clinicians should be aware of the potential factors influencing IGF-1 variability and take them into consideration when interpreting IGF-1 results 5, 6.
• Standardization of IGF-1 measurement is essential to ensure accurate and reliable results, particularly when switching from one platform to another 6.